Chapter 09
Physical Activity and Obesity
Physical Activity and Obesity
Definitions:
• Obesity: Having a very high amount of body fat
in relation to lean body mass, or Body Mass
Index (BMI) of 30 or higher.
• Body Mass Index (BMI): A measure of an adult’s
weight in relation to his or her height, specifically
the adult’s weight in kilograms divided by the
square of his or her height in meters.
Source = CDC
Physical Activity and Obesity
Obesity Trends Among U.S. Adults
between 1985 and 2010
Source of the data:
• The data shown in these maps were collected through
CDC’s Behavioral Risk Factor Surveillance System
(BRFSS). Each year, state health departments use
standard procedures to collect data through a series of
monthly telephone interviews with U.S. adults.
• Prevalence estimates generated for the maps may vary
slightly from those generated for the states by BRFSS as
slightly different analytic methods are used.
Source = CDC
Physical Activity and Obesity
Obesity Trends Among U.S. Adults
between 1985 and 2006
• In 1990, among states participating in the Behavioral Risk Factor
Surveillance System, 10 states had a prevalence of obesity less
than 10% and no states had prevalence equal to or greater than
15%.
• By 1998, no state had prevalence less than 10%, seven states had
a prevalence of obesity between 20-24%, and no state had
prevalence equal to or greater than 25%.
• In 2006, only four states had a prevalence of obesity less than 20%.
Twenty-two states had a prevalence equal or greater than 25%; Two
of these states (Mississippi and West Virginia) had a prevalence of
obesity equal to or greater than 30%.
• In 2009–2010, 35.7% of U.S. adults were obese.
Source = CDC
Physical Activity and Obesity
Obesity Trends* Among U.S. Adults
BRFSS, 1990, 1998, 2006, 2010
(*BMI 30, or about 30 lbs. overweight for 5’4” person)
1998
1990
2006
No Data
<10%
10%–14%
15%–19%
20%–24%
Physical Activity and Obesity
25%–29%
≥30%
Obesity Trends* Among U.S. Adults
BRFSS, 1985
(*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person)
No Data
<10%
10%–14%
Physical Activity and Obesity
Obesity Trends* Among U.S. Adults
BRFSS, 1988
(*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person)
No Data
<10%
10%–14%
Physical Activity and Obesity
Obesity Trends* Among U.S. Adults
BRFSS, 1991
(*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person)
No Data
<10%
10%–14%
15%–19%
Physical Activity and Obesity
Obesity Trends* Among U.S. Adults
BRFSS, 1994
(*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person)
No Data
<10%
10%–14%
15%–19%
Physical Activity and Obesity
Obesity Trends* Among U.S. Adults
BRFSS, 1998
(*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person)
No Data
<10%
10%–14%
15%–19%
≥20%
Physical Activity and Obesity
Obesity Trends* Among U.S. Adults
BRFSS, 2002
(*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person)
No Data
<10%
10%–14%
15%–19%
20%–24%
Physical Activity and Obesity
≥25%
Obesity Trends* Among U.S. Adults
BRFSS, 2004
(*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person)
No Data
<10%
10%–14%
15%–19%
20%–24%
Physical Activity and Obesity
≥25%
Obesity Trends* Among U.S. Adults
BRFSS, 2006
(*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person)
No Data
<10%
10%–14%
15%–19%
20%–24%
Physical Activity and Obesity
25%–29%
≥30%
Obesity Trends* Among U.S. Adults
BRFSS, 2008
(*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person)
No Data
<10%
10%–14%
15%–19%
20%–24%
25%–29%
≥30%
Obesity Trends* Among U.S. Adults
BRFSS, 2010
(*BMI ≥30, or ~ 30 lbs. overweight for 5’ 4” person)
No Data
<10%
10%–14%
15%–19%
20%–24%
25%–29%
≥30%
Obesity Trends Among U.S. Adults
Physical Activity and Obesity
Childhood Overweight
• BMI is used to Screen for Overweight in Children
• For children and adolescents (aged 2–19 years), the
result is plotted on the CDC growth charts to determine
the corresponding BMI-for-age percentile. Overweight is
defined as a BMI at or above the 95th percentile for
children of the same age and sex. This definition is
based on the 2000 CDC Growth Charts for the United
States. A child’s weight status is determined based on
an age- and sex-specific percentile for BMI rather than
by the BMI categories used for adults. Classifications of
overweight for children and adolescents are age- and
sex-specific because children’s body composition varies
as they age and varies between boys and girls.
Source = CDC
Physical Activity and Obesity
Trends in Childhood Overweight
Prevalence of Overweight* Among U.S. Children and Adolescents
(Aged 2 –19 Years)
National Health and Nutrition Examination Surveys
Physical Activity and Obesity
Trends in Childhood Overweight
Physical Activity and Obesity
Trends in Childhood Overweight
Physical Activity and Obesity
Trend Summary (2012)
Physical Activity and Obesity
Consequences of Childhood
Overweight
• Psychosocial Risks
• Some consequences of childhood and adolescent
overweight are psychosocial. Overweight children and
adolescents are targets of early and systematic social
discrimination. The psychological stress of social
stigmatization can cause low self-esteem which, in turn,
can hinder academic and social functioning, and persist
into adulthood
Source = CDC
Physical Activity and Obesity
Consequences of Childhood
Overweight
• Cardiovascular Disease Risks
• Overweight children and teens have been found to have
risk factors for cardiovascular disease (CVD), including
high cholesterol levels, high blood pressure, and
abnormal glucose tolerance. In a population-based
sample of 5- to 17-year-olds, almost 60% of overweight
children had at least one CVD risk factor while 25
percent of overweight children had two or more CVD risk
factors.
Source = CDC
Physical Activity and Obesity
Consequences of Childhood
Overweight
• Additional Health Risks
• Less common health conditions associated with increased weight
include asthma, hepatic steatosis, sleep apnea and Type 2 diabetes.
• Asthma is a disease of the lungs in which the airways become
blocked or narrowed causing breathing difficulty. Studies have
identified an association between childhood overweight and asthma.
• Hepatic steatosis is the fatty degeneration of the liver caused by a
high concentration of liver enzymes. Weight reduction causes liver
enzymes to normalize.
Source = CDC
Physical Activity and Obesity
Consequences of Childhood
Overweight
• Additional Health Risks
•
Sleep apnea is a less common complication of overweight for children and
adolescents. Sleep apnea is a sleep-associated breathing disorder defined
as the cessation of breathing during sleep that lasts for at least 10 seconds.
Sleep apnea is characterized by loud snoring and labored breathing. During
sleep apnea, oxygen levels in the blood can fall dramatically. One study
estimated that sleep apnea occurs in about 7% of overweight children.
•
Type 2 diabetes is increasingly being reported among children and
adolescents who are overweight. While diabetes and glucose intolerance, a
precursor of diabetes, are common health effects of adult obesity, only in
recent years has Type 2 diabetes begun to emerge as a health-related
problem among children and adolescents. Onset of diabetes in children
and adolescents can result in advanced complications such as CVD and
kidney failure.
Source = CDC
Physical Activity and Obesity
How to break the cycle?
Treating Childhood Obesity
• Change family lifestyle.
• Parents should be “agents of change” for
young children.
• Use behavior modification to support longterm change in behavior, including
modifying the environment (e.g., removing
cues to eat and adding cues to be active),
monitoring behavior, setting and checking
goals, and rewarding positive change.
Treating Childhood Obesity
• A review that compared lifestyle and drug
treatments for obesity in children and
adolescents found that 12 interventions,
centered on increasing physical activity or
reducing sedentary behaviors, had on average a
significant effect on reducing BMI after six or 12
months. The effect was small compared to
treatment with the drugs orlistat or
sibutramine,(withdrawn from market) but the
drugs had adverse side effects in the children
Treating Childhood Obesity
• Increase physical activity: have children do more
unstructured outdoor play; have them use active
transport (e.g., walking or bicycling) to school
and parks; provide transportation for sport
participation when needed; parents should
model an active lifestyle.
• Use nonconventional treatments, including
weight loss drugs, as an adjuvant to support
long-term lifestyle changes in adolescents who
are obese.
Treating Childhood Obesity
• Change dietary intake and eating patterns:
parents should model healthy food choices
and have children eat lower-fat and lowerenergy foods, increase fruits and
vegetables, decrease portion sizes, and
drink fewer sweetened beverages.
• Decrease time spent in sedentary
behavior (e.g., limit television viewing and
computer use to less than 2 h each day).
Consequences of Obesity In
Adults
• Overweight and obese individuals are at increased risk for many
diseases and health conditions, including the following:
• Hypertension (high blood pressure)
• Osteoarthritis (a degeneration of cartilage and its underlying bone
within a joint)
• Dyslipidemia (for example, high total cholesterol or high levels of
triglycerides)
• Type 2 diabetes
• Coronary heart disease
• Stroke
• Gallbladder disease
• Sleep apnea and respiratory problems
• Some cancers (endometrial, breast, and colon)
Source = CDC
Physical Activity and Obesity
Economic Burden of Obesity
• Article on the economic impact (burden) of obesity on
The United States
Obesity cost the United States an estimated $147
billion in 2008, nearly 10% of all medical costs
(Finkelstein et al. 2009). In a simulation model of
population data, medical costs of obesity were
higher than for smoking until people reached
their mid 50s, after which smokers had higher
costs. However, lifetime costs were still higher in
people who were obese because smokers died
at younger ages
Physical Activity and Obesity
Treatment of Obesity
• The NIH expert panel on obesity and overweight
(National Heart, Lung, and Blood Institute 1998) reached
these conclusions, though updates are expected in the
near future:
– Physical activity is a clinically accepted approach to weight loss,
as are low-calorie diets and lower-fat diets, behavior therapy,
pharmacotherapy, surgery, and combinations of these
techniques.
– For most overweight people, the initial goal of a prudent weight
loss program is to lose about 10% of weight over a period of six
months.
– After six months, the rate of weight loss usually declines, and
weight tends to stabilize at a plateau because of the reduction in
basal metabolic rate that results from the lower body mass
– Lost weight is usually regained unless a weight maintenance
program consisting of dietary therapy, physical activity, and
behavior therapy is continued indefinitely. After six months of
successful weight loss, efforts to maintain weight loss should be
undertaken.
Assessing and Defining Overweight
and Obesity
• Quetelet’s body mass index (BMI) and relative weight
are typically used to estimate overweight and obesity in
epidemiologic studies because they are easy to assess
in large numbers of subjects.
Patterning of Body Fat and
Disease Risk
• Excess fat in the abdomen out of proportion to total body fat is
another risk factor for chronic diseases associated with obesity.
• The waist-to-hip ratio predicts the patterning of visceral fat. Excess
fat above the waist, so-called android fat, increases risk for CHD
more than does excess fat below the waist, so-called gynoid fat. The
American Heart Association (2001) suggests that the desirable
waist-to-hip ratio is less than 1.00 for men and less than 0.80 for
women.
• Table 9.3 (next slide) illustrates the additive risk of increased
abdominal fat to the risk of BMI in the development of obesityassociated diseases in adults with a BMI of 25 to 34.9 kg/m2. Waist
circumference does not add to the accuracy of predicting disease
risk in people who have a BMI of 35 kg/m2 or more.
Patterning of Body Fat and
Disease Risk
The Consensus About Obesity
• In 1995, the National Heart, Lung, and Blood Institute’s
Obesity Education Initiative and the National Institute of
Diabetes and Digestive and Kidney Diseases assembled
an expert panel charged with the identification,
evaluation, and treatment of overweight and obesity in
adults. Their guidelines (based on 236 clinical studies), which
appeared in 1998 are as follows:
• Treatment of overweight is recommended only when patients have
two or more risk factors or a high waist circumference. Treatment
should focus on altering dietary and physical activity patterns to
prevent development of obesity and to produce moderate weight
loss.
Physical Activity and Obesity
The Consensus About Obesity
• Cardiovascular risk factors among obese people do not differ from
those for people of normal weight.
• Obese people who have at least three major CHD risk factors
usually require medical treatment aimed at risk reduction. Their CHD
risk is increased further if they are physically inactive and have high
serum triglycerides (>200 mg/dl), though the increased risk has not
been quantified.
• There is strong evidence that weight loss among people who are
overweight or obese reduces risk factors for diabetes and
cardiovascular disease (CVD). Weight loss reduces blood pressure
in both hypertensive and non hypertensive overweight individuals,
reduces serum triglycerides, increases HDL-C, and somewhat
reduces total serum cholesterol and low density lipoprotein
cholesterol (LDL-C). Weight loss reduces blood glucose levels in
overweight and obese people with and without diabetes and can
reduce glycosylated hemoglobin (HbA1c) in people with type 2
diabetes.
Metabolic Syndrome
• The American Heart Association and the National Heart,
Lung, and Blood Institute recommend that the metabolic
syndrome be identified as the presence of three or more
of these components (specific to population; U.S.
shown):
•Elevated waist circumference:
Men—equal to or greater than 40 in. (102 cm)
Women—equal to or greater than 35 in. (88 cm)
•Elevated triglycerides:
Equal to or greater than 150 mg/dl
Physical Activity and Obesity
Metabolic Syndrome
•Reduced HDL (“good”) cholesterol:
Men—less than 40 mg/dl
Women—less than 50 mg/dl
•Elevated blood pressure:
Equal to or greater than 130/85 mmHg
•Elevated fasting glucose:
Equal to or greater than 100 mg/dl
Obesity is considered a disease, there is controversy about whether it
is an independent cause of premature death or whether it is deadly
because of the constellation of risk factors for mortality that
accompanies obesity (Metabolic Syndrome)
Etiology of Overweight and
Obesity: Set Point or settling Point?
• Two common theories about the etiology
of overweight and obesity, set point and
settling point, address how physical
activity can play a role in the treatment or
prevention of overweight and obesity.
Physical Activity and Obesity
Set Point Theory
• Set point theory hypothesizes that the body has
an internal control mechanism, that is, a set
point, located in the lateral hypothalamus of the
brain, that regulates metabolism to maintain a
certain level of body fat.
• Though evidence in rats has supported the
theory, there is no scientific consensus that such
a metabolic set point exists in humans for fat
maintenance.
Physical Activity and Obesity
Settling Point Theory
• Weight loss and gain in most humans are more
related to the patterns of diet and physical
activity that people “settle” into as habits based
on the interaction of their genetic dispositions,
learning, and environmental cues to behavior.
• Evidence suggests that obese people are more
sensitive to food-related stimuli in the social and
physical environment, which influence their
energy intake, than to the stimuli for energy
expenditure
Physical Activity and Obesity
The Role of Physical Activity
• Physical activity has an important role in the prevention
and treatment of overweight and obesity, even if that role
is not yet completely understood.
• Prevention of obesity in children should focus on
increasing vigorous physical activity rather than
restricting energy intake
• Evidence shows that regular physical activity or physical
fitness can (1) reduce health risks in people who are
overweight, (2) protect against excessive weight gain, (3)
help overweight and obese people lose weight, and (4)
help people maintain stable weight after they lose it.
Physical Activity and Obesity
Physical Activity and Fitness and the
Health Risks of Obesity: The Evidence
• Physical Activity Studies on the joint association
of self-reported physical activity and high BMI
typically show that each is an independent risk
factor for all-cause mortality and mortality from
CVD and cancer.
• The mortality risk of obesity is not eliminated by
physical activity, but it was usually reduced
substantially in population cohorts that did not
initially have a chronic disease.
Physical Activity and Obesity
Physical Activity and Overweight or
Obesity: The Evidence
Physical Fitness
• Lipid Research Clinics Mortality Study
• examined the prospective associations of fitness
and BMI with mortality risk in 1359 Russian men
and 1716 U.S. men aged 40 to 59 years who
were followed for 18 to 23 years
• fitness eliminated the risks of obesity in Russian
men; but in American men, fitness and fatness
were associated with mortality independently of
each other
Physical Activity and Obesity
Physical Activity and Overweight or
Obesity: The Evidence
Physical Fitness
• Aerobics Center Longitudinal Study
– Association of fitness with reduced risk of
CVD and all-cause mortality was independent
of overweight
– When all other variables were accounted for,
fitness level was the determining factor for
relative risk. BMI variance in each fitness
category did not change the relative risk (see
Figure 9.8, next slide)
Physical Activity and Obesity
Figure 9.8 - Aerobics Center Longitudinal Study with 21,856 men followed for
approximately eight years. a total of 21,925 men aged 33 to 83 years were followed
and men with abnormal ECG or history of myocardial infarction, stroke, or cancer
excluded. results were adjusted for age, examination year, smoking, alcohol intake,
and parental history of coronary heart disease
Physical Activity and Overweight or
Obesity: The Evidence
Physical Fitness
• Women’s Ischemia Syndrome Evaluation
(WISE)
• From 1996 to 2000, 936 women were enrolled at four U.S.
academic medical centers when clinical evaluation and
angiography indicated they had myocardial ischemia At
enrollment, 76% were overweight.
• Overweight women were more likely than normal weight
women to have CAD risk factors, but BMI and girth measures
were not associated with CAD or cardiovascular events after
adjustment for other risk factors. Lower fitness scores at entry
were 80% more likely to have CAD risk factors
Physical Activity and Obesity
Physical Activity and Overweight or
Obesity: The Evidence
Fit But Fat ?
A recent large study using pooled data from 19 prospective
studies of 1.46 million white adults, 19 to 84 years of
age, observed that after taking biases from smoking and
ill health into consideration and adjusting for physical
activity, there was a J-shaped relationship between BMI
and all-cause mortality (Berrington de Gonzalez et al.
2010). The highest mortality rates occurred at BMI of
40.0 to 49.9 kg/m2 and the lowest generally at 20.0 to
24.9 kg/m2.
The evidence is clear that physical activity can favorably
modify the impact of overweight and moderate obesity
on several health risk factors, including metabolic
syndrome
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• A review of 11 prospective cohort studies concluded that
physical activity or increased fitness measured by
maximal treadmill endurance is associated with
minimizing weight gain or with a reduction in the risk of
large weight gains (e.g., 5-10 kg) among adults over
periods ranging from two to 10 years
• The optimal amount of physical activity needed for
weight maintenance (<3% change in body weight) over
the long term is unclear, but that many people may need
more than 150 min of moderate-intensity activity each
week to maintain their weight at a stable level
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• Finnish Cohort Study
– Risk of weight gain (5kg) was elevated in
subjects with little leisure-time activity
– The prevalence of obesity was inversely
associated with physical activity
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• NHANES I Follow-up Study
– A low-level of physical activity was strongly related to
major weight gain (13 kg)
– The relative risk (RR) of major weight gain from the
lowest to highest fit group was 3.1 for men, and 3.8
for women
– The RR was 2.3 for men and 7.1 for women if they
reported low levels of physical activity in both the
initial and follow-up survey.
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• Nurses Health Study
– Those women who quit smoking and did not
change their physical activity levels gained
2.3 kg vs. those who continued to smoke
– Those women who quit smoking and
increased their physical activity only gained
between 1.3-1.8 kg (weight gain prevention).
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• The Coronary Artery Risk Development in
Young Adults (CARDIA) Study
– Examined both men and women, white and black
adults.
– Decreased physical fitness is strongly associated with
weight gain in both sexes
– Each 1 minute decrease in maximal treadmill
endurance translated into 1.5 kg weight gain in men
and 2.1 kg in women
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• U.S. Male Health Professionals
– Middle-aged men who increased physical activity lost
an average weight of 1.4 kg compared to a weight
gain of 1.4 kg in the entire cohort.
– The prevalence of obesity was the lowest in those
who maintained vigorous activity
– Each 1.5 hour increase in weekly vigorous activity
predicted a 2-kg weight loss in middle-aged men
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• American Cancer Society: Cancer Prevention
Study I and II (see also Figure 9.9, next slide)
• A cohort of healthy, non-Hispanic white men (n =35,156)
and women (n = 44,080) aged 50 to 74 years who had
self reported BMI (kg/m2) of 18 to 32 were questioned in
1982 and 1992 about their weight and participation in 10
leisure time physical activities and home chores
• Smaller gains in BMI among men and women who were
most active compared to inactive
• Protection of weight gain less among those who initially
presented overweight
Physical Activity and Obesity
Figure 9.9 - Consistent leisure-time physical activity and 10-year body
mass gain in normal-weight Americans.
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
Study of Women’s Health Across the Nation
(SWAN)
• This was a prospective study of the associations of
weight and waist circumference with physical activity
around the period of menopausal transition among 3064
racially and ethnically diverse U.S. women aged 42 to 52
years
• Maintaining or increasing physical activity levels helped
protect against midlife increases in body weight and girth
that women commonly experience.
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• Sweden Study
• The association of moderate-to-vigorous exercise two or
more days a week with BMI was examined over eight
years
• In both men and women, those who did not exercise had
an increase in BMI
• Men who said they exercised at baseline but not at
follow-up had a larger increase in BMI than men who
exercised at both baseline and at follow-up.
• Women who did not exercise at either baseline or followup had an increase in compared to women who
exercised both at baseline and follow-up.
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• Norway Nord-Trøndelag Health Study: HUNT 1
and HUNT 2 (see also Figure 9.10, next slide)
• Longitudinal study of an entire county in Norway
examined whether leisure-time physical activity could
predict change in BMI measured 11 years later
• Weight gain was greater among inactive men and
women, but physical activity had a modest impact on
slowing weight gain in healthy, normal-weight adults.
Figure 9.10 - Leisure-time physical activity and 11-year weight gain in normalweight Norwegian adults.
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• Aerobics Center Longitudinal Study
– Change in fitness predicted weight gain or loss
between repeat weight measurements over 7.5 yrs.
– Fitness reduced the risk of weight gain (10 kg) by
more than 20% in both men and women
– Fitness reduced the risk of weight gain (5 kg) by more
than 10 – 15 % in both men and women
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• The Framingham Children’s Study (FCS)
• This longitudinal study of childhood cardiovascular risk behaviors
began in 1987 with a small cohort of 106 healthy children aged 3 to
5 years who were third- and fourth-generation offspring of the initial
Framingham Study cohort.
• An eight year follow-up of 94 children found that boys and girls in the
highest one-third of average daily activity from ages 4 to 11 years
had smaller gains in BMI and skinfold thickness throughout
childhood than the other children
• The difference was most pronounced in girls. By age 11, BMI was
about 7% lower and skinfold thickness about 20% lower in the most
active children.
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• American Indian Schoolchildren – PATHWAYS
• A cohort of 454 American Indian schoolchildren was
followed for three years from 2nd to 5th grade
• skinfolds and bioelectrical impedance were used to
estimate percent body fat
• higher levels of total physical activity (recorded from
accelerometer counts) predicted lower percentage body
fat by 5th grade among normal-weight children but not
overweight children.
• Although an objective measure of physical activity was
used in this study, it was performed for only one day of
observation. Also, skinfolds, bioelectrical impedance,
and BMI are imprecise measures of body fatness.
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• Avon Longitudinal Study of Parents and Children
(ALSPAC)
• Ongoing birth cohort study with data collected between 2003 and
2007 that examined associations between children’s physical
activity at age 12 and their body fatness at age 14
• Total and moderate-to-vigorous physical activity (measured by an
accelerometer for seven days) at age 12 was predictive of body fat
mass (measured by DXA) at age 14.
• An extra 15 min of moderate-to-vigorous physical activity per day at
age 12 was associated with lower fat mass at age 14 in boys (by
11.9% [95% CI: 9.5-14.3%]) and girls (by 9.8% [6.7-12.8%]).
Physical Activity and Obesity
Physical Activity and Prevention of
Excess Weight Gain: The Evidence
• The Women’s Health Study (WHS)
• The WHS was a randomized trial testing low-dose aspirin and
vitamin E for preventing CVD and cancer among healthy women,
conducted between 1992 and 2004. A recent analysis examined the
association of different amounts of physical activity with long-term
weight changes among women consuming a usual diet.
• The findings from this large study with long follow-up provide
support for the conclusion of the scientific advisory committee for the
Physical Activity Guidelines for Americans—that many individuals
may need more than 150 min of moderate-intensity activity each
week to maintain their weight at a stable level
Physical Activity and Weight
Loss: The Evidence
• It is paradoxical that at the same time the prevalence of obesity in
the United States was increasing, more adults were engaging in
voluntary weight loss
• A recent systematic, quantitative review evaluated 18 prospective
cohort studies of mortality risk after intentional weight loss by
change in diet or physical activity
• Fourteen of the studies adjusted for physical activity, but the studies
did not clarify the relative contributions of diet or physical activity to
weight loss or to mortality risk. The authors concluded that there
was a need for well-designed studies to identify the independent
and interactive effects of physical activity, diet, and body
composition in populations most likely to increase longevity through
weight loss.
Physical Activity and Obesity
Physical Activity and Weight
Loss: The Evidence
• Weight Cycling: Aerobics Center Longitudinal Study
(ACLS)
• Weight cycling status was defined as five or more episodes of losing
at least 2.3 kg.
• Even though a history of weight cycling did not increase the risk of
long-term weight gain, cardiorespiratory fitness at baseline and
increased fitness over the follow-up were associated with less
weight gain in both women and men
• For each extra 1 min of endurance on a maximal treadmill test at
baseline, or for each 1-min increase in endurance between clinic
visits (a difference of 7% in women and 5% in men), initial weight or
weight gain was 0.2 kg lower for women and 0.55 kg lower for men.
Physical Activity and Obesity: The
Evidence – Exercise Training Studies
• Although physical activity has great potential efficacy for
reducing body fat mass, studies have found that its
actual effectiveness is small.
• The American Dietetic Association recently concluded
that few studies have used a large enough “dose” of
physical activity to achieve a 5% weight loss with a
physical activity intervention alone.
• There is emerging evidence, though, that regular
physical activity can have favorable effects on abdominal
obesity and excess fat stored in the liver and skeletal
muscle when its effects on body weight or total fat mass
are minimal
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise Training Studies
• Exercise ONLY
• A recent meta-analysis evaluated 14 aerobic exercise
trials that lasted three to 12 months and involved 1847
obese or overweight patients. Six-month and 12-month
programs similarly were associated with modest
reductions in weight of 1.6 and 1.7 kg and waist
circumference of about 2 cm
• Some other well-designed trials have shown benefits of
exercise on abdominal obesity or have combined
physical activity with diet for favorable weight-related
outcomes.
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise Training Studies
• The Midwest Exercise Trial
• 16-month randomized controlled trial tested
whether supervised, moderate-intensity exercise
without dieting was effective for losing weight or
preventing weight gain in young adults who were
overweight
• Exercise prevented weight gain in women and
produced weight loss in men. (see Figure 9-11, next
slide)
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise Training Studies
Figure 9.11 Results of the Midwest Exercise Trial showed that 16 months of
exercise reduced body weight and percent body fat without dieting in overweight
men and women
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise Training Studies
• Fred Hutchinson Cancer Research Center—
Seattle
• This 12-month trial examined the effect of
moderate - to vigorous aerobic exercise in
sedentary men and women
• Weight loss was less than expected, so the
study shows that people tend to eat more when
they exercise more, a practical problem of using
exercise alone for short-term weight loss.
Physical Activity and Obesity: The
Evidence – Exercise Training Studies
• Duke University—STRRIDE Trial
• One hundred seventy-five sedentary, overweight men and women
(average BMI of 30 kg/m2) with dyslipidemia were randomly
assigned to participate for six months in a control group or for eight
months
• People in the control group had a 1% increase in body weight and
an 8.6% increase in intra-abdominal fat, while the two exercise
groups that expended about 14 kcal/kg each week had about a 1%
decrease in body weight.
• The highest dose of exercise (i.e., about 23 kcal/kg each week)
produced a nearly 3% decrease in weight and 7% decreases in
intra-abdominal fat and subcutaneous abdominal fat without
changes in caloric intake
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise Training Studies
• Minnesota Strength Training in Women Study
• Sixty middle-aged women who had a BMI between 20 and 35 kg/m2
were randomly assigned to 15 weeks of twice weekly supervised
strength training, followed by six months of unsupervised training, or
to a no-intervention control group
• 39 weeks of follow-up, there was no effect of strength training on
weight change, but the exercise group had changed the composition
of their body weight (They gained 0.89 kg more fat-free mass, lost
1.0 kg more fat mass, and lost 1.63% more percent body fat
compared to the control group who did not exercise.)
• This study shows not only that resistance training can be effective in
helping women lose body fat but also why it is wrong to judge the
effectiveness of exercise by body weight alone.
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise Training Studies
• University of Virginia
• The effects of exercise training intensity on abdominal fat
and body composition were tested in 27 middle-aged
obese women (BMI = 34 ± 6 kg/m2) with metabolic
syndrome
• Women were assigned different exercise intensities
• Computed tomography scans were used to determine
abdominal fat. Percent body fat was assessed by air
displacement plethysmography.
• High-intensity training, but not low-intensity training,
reduced total abdominal fat, subcutaneous abdominal
fat, and intra-abdominal fat.
Physical Activity and Obesity: The
Evidence – Exercise Plus Diet
• The scientific advisory committee for the
Physical Activity Guidelines for Americans
concluded that adults who want to lose more
than 5% of their body weight through an
exercise program must also keep their food
intake constant or restrict it through diet (Physical
Activity Guidelines Advisory Committee 2008). Several studies
have shown that this can be effective in people
who are overweight or obese.
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise Plus Diet
• Women’s Healthy Lifestyle Project
• This was a five-year randomized controlled trial of a
dietary and physical activity lifestyle intervention
• Women in the lifestyle intervention group were more
physically active and reported eating fewer calories than
controls during the study period (see Figure 9.12, next
slide).
• Percent body fat measured by skinfolds and DXA
decreased by 0.5% in the diet plus physical activity
group while increasing by 1% in the control group. Waist
circumference decreased more in the intervention group
than in controls.
Physical Activity and Obesity: The
Evidence – Exercise Plus Diet
Figure 9.12 The Women's Healthy Lifestyle Project showed that increased physical
activity and decreased calorie intake prevented five-year weight gain in
perimenopausal women
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise Plus Diet
• St. Luke’s–Roosevelt Hospital, New York City
• Moderately obese patients aged 19 to 48 years received weekly
nutrition counseling and were randomly assigned to one of three
groups for eight months: diet plus strength training (progressive
resistance for arms and legs), diet plus aerobic training (leg and arm
cycling), or diet only
• All groups lost about 9.0 kg.
• The strength training group lost less fat-free mass than the aerobic
and diet-only groups but nonetheless had a similar drop in RMR.
Thus, strength training protected lean mass during dieting but did
not prevent the decline in RMR commonly seen when overweight
people lose weight.
Physical Activity and Obesity: The
Evidence – Behavioral Factors
• The Dose-Response to Exercise in Women
(DREW) trial results showed that even though
the exercisers were asked to keep their normal
diet, most of the women who exercised ate more
than they had before starting the trial.
• This illustrates the practical problems of gauging
the impact of exercise on weight loss, as people
may eat more than normal or decrease daily non
exercise activities when they undertake a new
exercise program.
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise and Appetite
• The brain senses blood levels of glucose and
insulin and regulates hunger between meals.
Low glucose stimulates appetite, while high
levels of glucose and insulin inhibit appetite.
• Exercise lowers insulin and glucose levels, so it
might affect appetite. Whether exercise
stimulates or inhibits appetite in the short term
has not as yet been clearly determined, but
studies generally show that appetite is
suppressed shortly after an exercise session
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise and Appetite
• “Leptin and ghrelin are two hormones that have
been recognized to have a major influence on
energy balance. Leptin is a mediator of longterm regulation of energy balance, suppressing
food intake and thereby inducing weight loss.
Ghrelin on the other hand is a fast-acting
hormone, seemingly playing a role in meal
initiation.” Source Article “The role of leptin and
ghrelin in the regulation of food intake and
body weight in humans: a review.”
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise and Appetite
• High leptin levels induce feelings of satiety via
the hypothalamus.
• Obese have high levels of circulating leptin but
appear to be leptin resistant. Levels return to
normal following weight loss
• Ghrelin is secreted by the stomach and
pancreas to stimulate appetite, and increases
before, decreases after meals. Ghrelin is
increased after long duration exercise
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Exercise and Appetite
• Suppression of appetite by these hormone
activities seem to be more effective in men than
women, based on a limited number of research
studies.
• Women’s feelings of hunger were suppressed
during a session of walking that expended 550
kcal, but they were not affected between meals
despite an increase in ghrelin and a delayed and
short-term decrease in leptin after exercise
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Genetic Factors
• An association has been found for the FTO (see
section on “Association with Obesity”) gene. People of
European ancestry who inherit a risky variation
in the FTO gene from one or both parents (3050% of the populations studied) weigh on
average 1 to 4 kg more and have a 15% to 65%
increased risk of having high BMI, perhaps
because the gene contributes to eating more or
storing more fat.
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Genetic Factors
• The population attributable risk of obesity from variations
in the FTO gene has been shown to be about 20%
• Physical activity has been associated with lower BMI in
people who have a risky version of the FTO gene in
several studies, but not all.
• Despite the likelihood that physical activity will interact
with people’s genes to influence obesity-related
outcomes, some studies seem to show that physical
activity habits during adulthood influence obesity just as
strongly as, or more strongly than, genetic inheritance or
childhood habits.
• Persistent physical activity reduces odds of weight gain
even after genes and childhood environment are partially
controlled.
Physical Activity and Obesity: The
Evidence – Calories, Exercise
• The amount of weight loss with physical activity is
additive to the loss that follows a reduction in calorie
intake with a diet.
• Because physical activity, especially resistance
exercise, can decrease the percentage of body
mass that is fat while increasing fat free mass, it has
the potential to retard the reduction in BMR common
during restrictive diets.
• Exercise can lead to a small gain in fat-free mass as
body fat is reduced; this occurs when body weight
does not change during the exercise program.
Physical Activity and Obesity: The
Evidence – Calories, Exercise
• People who desire to increase or maintain fatfree mass during an exercise program must
have a diet of sufficient calories to balance the
increased energy expenditure.
• In one study of obese women (You et al. 2006),
only diet plus exercise, not diet alone,
decreased the size of subcutaneous fat cells in
the abdomen, a risk factor for type 2 diabetes.
Physical Activity and Obesity: The
Evidence – Weight Maintenance
• Lost body weight is usually regained when diets are
used alone, but diet combined with increased exercise
seems to yield better maintenance of weight loss,
especially if the exercise program is maintained after the
diet ends.
• Figure 9.13 (next slide) illustrates the results of an eightweek diet among obese adults. Not only was exercise as
effective as diet for weight loss, but adding an exercise
program at the end of the diet also prevented
participants from regaining weight eight and 18 months
later.
Physical Activity and Obesity: The
Evidence – Weight Maintenance
Figure 9.13 Study on moderately obese people illustrates not only that exercise was
as effective for weight loss as an eight-week diet among adults, but also that adding
an exercise program at the end of a diet prevented participants from regaining
weight later.
Physical Activity and Obesity
Physical Activity and Obesity: The
Evidence – Weight Maintenance
• The amount of physical activity needed to keep weight
off after a diet is not fully known, but experts have
suggested it may be as much as 2500 to 2800
kcal/week, two to three times as much as recommended
for reducing other health risks
• Many correlation studies show a strong association
between physical activity at follow-up and maintenance
of a weight loss
• much of the lost weight is regained after exercise
interventions end, and a high level of daily physical
activity may be necessary to prevent weight regain
Strength of the Evidence
• Both population-based epidemiological
studies and clinical trials support the claim
that regular physical activity and exercise
training are useful for reducing the primary
and secondary risk of excess weight gain
during adulthood and for helping obese or
overweight people keep off most of the
weight they lose after a weight loss
intervention.
Physical Activity and Obesity
Strength of the Evidence
• Temporal Sequence
– An increase in physical fitness (defined as an
increase in treadmill time) predict weight loss
or stopping weight gain over periods of 2-10
years
Physical Activity and Obesity
Strength of the Evidence
• Strength of the Association
– Expending 1,100 kcal/wk show mean
reductions of 0.06 kg (0.13 lbs) of fat weight
per week.
– Expending 2,200 kcal/wk show mean
reductions of 0.21kg (0.46 lbs) of fat weight
per week.
– Thus, higher energy expenditures are
associated with greater fat loss.
Physical Activity and Obesity
Strength of the Evidence
• Consistency
– Exercise training contributes to weight and fat
loss in both men and women regardless of
race
– Physical activity and fitness level also reduce
mortality risk in people who are overweight.
Physical Activity and Obesity
Strength of the Evidence –
• Dose Response
– Fat loss is linearly dependent on the amount
of energy expenditure in short term studies
– This finding is not reproducible in long term
studies because of poor subject adherence to
exercise
– Effective exercise programming would include
long duration (60 + minutes of walking) and
high caloric expenditure (2000 kcal /week) at
55% or higher intensity
Physical Activity and Obesity
Strength of the Evidence
• Biological Plausibility
– Energy expenditure can be increased up to 20
times basal metabolism during exercise,
promoting a negative energy balance
– Depending upon the intensity of exercise,
post-exercise energy expenditure may
increase
– Increasing lean mass will increase BMR,
exercise helps to maintain lean mass.
Physical Activity and Obesity
Strength of the Evidence
• Biological Plausibility
• Resistance exercise training can increase basal
metabolic rate by an extra 50 to 75 kcal on
average. Most of the increase is explained by
increased nonfat body mass, not by extra use of
protein as fuel.
• Increased physical activity and better nutrition
have been shown to normalize glucose and lipid
blood profiles in the absence of significant
weight loss in many individuals.
How Does Exercise Help People
Lose Body Fat?
• Increases energy expenditure
• Retards loss of muscle mass, hence
maintaining BMR
• Increases metabolic rate during and after
exercise
• Possibly increases SNS activity in people
who have abnormally low tonic activity of
the sympathetic nervous system
How Does Exercise Help People
Lose Body Fat?
• Possibly suppresses appetite acutely after
exercise, though overall appetite tends to
increase with chronic increases in physical
activity
• Offsets effects of weight cycling (yo-yo
dieting)
• Has positive psychological effects that
help people adhere to dietary or exercise
programs
Final Thoughts
• Weight Loss or risk reduction? Most individuals judge the
success of diet and exercise by scale weight. Rates of
weight loss with a successful program average
approximately 1 kg per week, which is viewed by many
as frustratingly slow progress. Hence, dropout rates can
be high within the first three to six months of a weight
loss or exercise program. A change from preoccupation
with scale weight to healthful management of blood
pressure, blood glucose, and blood lipid levels through a
prudent diet and regular physical activity in pursuit of
moderate physical fitness is perhaps a more important
health goal for most people who are overweight but not
obese.
End of Presentation
Physical Activity and Obesity